PIC18F2450-ESLASHP datasheet(35/320 Pages) MICROCHIP

35 / 320 page

PIC18F2450/4450

Advance Information

DS39760A-page 33

3.0

POWER-MANAGED MODES

PIC18F2450/4450 devices offer a total of seven

operating

modes

for

efficient

power

management. These modes provide a variety of

options for selective power conservation in applications

where resources may be limited (i.e., battery-powered

devices).

There are three categories of power-managed modes:

• Run modes

• Idle modes

• Sleep mode

These categories define which portions of the device

are clocked and sometimes, what speed. The Run and

Idle modes may use any of the three available clock

sources (primary, secondary or internal oscillator); the

Sleep mode does not use a clock source.

The power-managed modes include several power-

saving

features

offered

PICmicro®

devices. One is the clock switching feature, offered in

other PIC18 devices, allowing the controller to use the

Timer1 oscillator in place of the primary oscillator. Also

included is the Sleep mode, offered by all PICmicro

devices, where all device clocks are stopped.

3.1

Selecting Power-Managed Modes

Selecting

power-managed

mode

requires

two

decisions: if the CPU is to be clocked or not and the

selection

clock

source.

The

IDLEN

bit

(OSCCON<7>) controls CPU clocking, while the

SCS1:SCS0 bits (OSCCON<1:0>) select the clock

source. The individual modes, bit settings, clock sources

and affected modules are summarized in Table 3-1.

3.1.1

CLOCK SOURCES

The SCS1:SCS0 bits allow the selection of one of three

clock sources for power-managed modes. They are:

• The primary clock, as defined by the

FOSC3:FOSC0 Configuration bits

• The secondary clock (the Timer1 oscillator)

• The internal oscillator (for RC modes)

3.1.2

ENTERING POWER-MANAGED

MODES

Switching from one power-managed mode to another

begins

the

OSCCON

The

SCS1:SCS0 bits select the clock source and determine

which Run or Idle mode is to be used. Changing these

bits causes an immediate switch to the new clock

source, assuming that it is running. The switch may

also be subject to clock transition delays. These are

discussed in Section 3.1.3 “Clock Transitions and

Status Indicators” and subsequent sections.

Entry to the power-managed Idle or Sleep modes is

triggered by the execution of a SLEEP instruction. The

actual mode that results depends on the status of the

IDLEN bit.

Depending on the current mode and the mode being

switched to, a change to a power-managed mode does

not always require setting all of these bits. Many

transitions may be done by changing the oscillator

select bits, or changing the IDLEN bit, prior to issuing a

SLEEP

instruction. If the IDLEN bit is already

configured correctly, it may only be necessary to

perform a SLEEP instruction to switch to the desired

mode.

TABLE 3-1:

POWER-MANAGED MODES

Mode

OSCCON Bits

Module Clocking

Available Clock and Oscillator Source

IDLEN(1)

SCS1:SCS0

CPU

Peripherals

Sleep

N/A

Off

None – all clocks are disabled

PRI_RUN

N/A

Clocked

Primary – all oscillator modes.

This is the normal full power execution mode.

SEC_RUN

N/A

Clocked

Secondary – Timer1 oscillator

RC_RUN

N/A

Clocked

Internal oscillator(2)

PRI_IDLE

100

Off

Clocked

Primary – all oscillator modes

SEC_IDLE

101

Off

Clocked

Secondary – Timer1 oscillator

RC_IDLE

11x

Off

Clocked

Internal oscillator(2)

Note 1:

IDLEN reflects its value when the SLEEP instruction is executed.

Clock is INTRC source.

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